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What's the context surrounding this? Homework problem? Real-life system test? Exercise out of a book? Some sort of online challenge?
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ReidAug 2 '13 at 14:05

This question appears to be off-topic because it's more suitable for SO, and even so it shows minimal research
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rathAug 3 '13 at 4:57

1 Answer
1

Including solutions that collect statistical information, there are several solutions which are used during cryptographic analytics that can cope with shifting (read: changing) values, frequencies, and pattern detections.

Yet, merely having knowledge of the cyphertext will not be enough most of the time. For example, it's not really helpful when a modern encryption algorithm has been used since such algorithms twist and mix the bits so that it is "near to impossible" to trace or guess how a single bit (or byte) of the message was encrypted.

exploiting partial break

Additionally, you have to count in that - due to the fact your example shows you have part of the plain-text which was used to generate the encrypted message - there are additional hints for analysts that could show how the encrypted message may have been encrypted. This in itself weakens the encrypted text in this specific situation, as it represents a "partial break" which can be build upon.

practical approach

I could go on and practically approach your example to show you step-by-step how I would be able to decode your encrypted message, but while writing this answer I have decided to not do that to prevent going off-topic, because:

analyzing or decyphering a block of data are off-topic here, as the results are rarely useful to anyone else.